A methodological and performance comparison of free weight and smith-machine jump squats

In many cases, isoinertial strength and power testing of the lower body is conducted using a jump squat movement in an apparatus involving a barbell attached to vertical supports (Smith-machine apparatus). As a result the Smith-machine restricts movement of the barbell to the vertical plane and potentially decreases variability in performing the movement. However, this assertion is yet to be investigated. Eighteen elite male volleyball players (19.6 ± 2.6 years, 2.00 ± .07 m, 91.5 ± 8.8 kg) performed jump squats with a low (body mass + 25% body mass) and moderate (body mass +50% body mass) load using both a Smith-machine and with free weight. Assessments were conducted on the repeatability of the conditions as test protocols, and to compare the kinetic and kinematic differences between the two conditions. Both conditions demonstrated excellent reliability (ICC > 0.80) and acceptable variability (%CV <5.00) and were similar for most variables (% co-variance 0.60-4.94), with the exception of mean power (% co-variance 11.06-17.62). Only mean power was found to be dissimilar between conditions (p=0.000), with the free weight condition producing superior mean power values (ES=0.60-1.41). No other differences were observed. The results of this study suggest that both conditions are acceptable methods of assessing the lower body for strength and power qualities, but that some kinetic values may differ as a result of the testing procedures. It is important to note that this research used elite national-level volleyball players as its participants; as such care must be taken when applying these results outside this population.